BACKGROUND: Autoimmune pancreatitis is an IgG4-related fibroinflammatory condition often associated with obstructive jaundice, as most lesions are located at the head of the pancreas. IgG4 level can help in the diagnosis, but it is normal in nearly 30% of affected patients.

CASE REPORT: A 55-year-old woman presented with a 5-month history of 20-pound unintentional weight loss and intermittent abdominal pain. She had an unremarkable abdominal exam and significant findings included a small, non-mobile rubbery left axillary lymph node. Complete blood count, complete metabolic panel, amylase, anti-smooth muscle antibody, antimitochondrial antibody, carcinoembryonic antigen, Ca 19-9, complement C3 and C4, antinuclear antibody, anti-Smith double-strand antibody, and IgG4 were all within normal limits. CT of the abdomen showed a mass in the junction of the body and tail of the pancreas and endoscopic ultrasound showed it as encasing the splenic artery. Fine-needle aspiration cytology demonstrated follicular hyperplasia, obliterative phlebitis, storiform fibrosis, and negative staining for IgG4 and malignancy. Left axillary lymph node biopsy demonstrated follicular hyperplasia. PET scan revealed hypermetabolic uptake of the pancreas tail, bone marrow, and spleen, as well as diffuse lymphadenopathy. Bone marrow biopsy showed follicular hyperplasia and was negative for malignancy. The patient was started on 40 mg of oral prednisone for possible autoimmune disease. During follow-up, she reported progressive improvement and a repeat PET scan 6 months later showed marked improvement.

CONCLUSIONS: A normal IgG4 value should not decrease the clinical suspicion of IgG4-related disease. If clinical, histological, and radiological findings coincide, glucocorticoids should be initiated with subsequent follow-up to evaluate for a response.

Keywords: Antibodies, Anti-Idiotypic - metabolism, Autoimmune Diseases - metabolism, Biopsy, Fine-Needle, Diagnosis, Differential, Immunoglobulin G - immunology, Pancreas, Pancreatitis - metabolism, Positron-Emission Tomography, Tomography, X-Ray Computed